Solution
standard deviation =s = =23
Margin of error = E = 5
At 95% confidence level the z is ,
= 1 - 95% = 1 - 0.95 = 0.05
/ 2 = 0.05 / 2 = 0.025
Z/2 = Z0.025 = 1.96
sample size = n = [Z/2* / E] 2
n = ( 1.96*23 /5 )2
n =81.288
Sample size = n =81
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